1. Technical Field
The present invention belongs to the technical field of air sterilization and purification and in particular relates to a plasma air sterilizing and purifying device and an air sterilizing and purifying method thereof.
2. Description of Related Art
According to the types of air disinfection factors, the existing air sterilizing and purifying devices are classified into the following six major types: filtering absorption type, electrostatic absorption type, high-energy ion sterilization and purification type, ultraviolet sterilization and purification type, photo-catalytic purification type, and plasma sterilization and purification type; the air sterilizing and purifying method is realized by driving the indoor air to flow through the air sterilizing and purifying device.
The filtering absorption type air sterilizing and purifying device absorbs the suspended particle contaminants and harmful gases in the airflow by means of the Van der Waals' force to realize air purification. This kind of device has the following defects: it exclusively filters dust and cannot perform sterilization; the filtering resistance is increased along with the accumulation of the dust particles, with the dust capacitance reduced and the purification efficiency lowered. The filter screen needs to be cleaned or replaced in time; otherwise, secondary pollution will be caused.
The electronic static absorption type air sterilizing and purifying device separates the particles from the air flow by means of the Coulombic force via the static discharge of an electrode to fulfill the aim of air purification. This kind of device can clear the dust but has a bad sterilization effect and fails to efficiently purify the air and to remove harmful gases such as formaldehyde.
The high-energy ionic sterilizing and purifying device applies a high-frequency electric field onto two electrodes which are isolated by a media to discharge along the plane, and the charges react with the molecules in the air to generate ozone and other substances. This kind of device works by means of the instability and strong oxidation effects of ozone. Ozone is a strong oxidizer which cannot be stored in a site in direct contact with inflammable and explosive gases and cannot gather dust. Once ozone leaks, the respiratory tract of the human body will be injured.
The ultraviolet air sterilizing and purifying device uses a low-pressure mercury vapor discharge lamp to radiate ultraviolet rays with a wavelength of 253.7 nm under the action of high voltage so as to kill microbes such as bacteria and viruses. The ultraviolet rays are invisible light and easily leak and injure the eyes and skin of the human body; the lifespan of the ultraviolet tube is generally less than 8,000 hours. The mentioned defect is one of the reasons that hospitals rarely adopt this kind of device.
The principle of the optical-catalytic purification technology is as follows: under the irradiation of the ultraviolet rays with a wavelength of 387.5 nm, the electrons in the dielectric belt of the photo-catalyst TiO2 are excited to enter the conductive belt to generate corresponding cavities. When the indoor air flows through the surface of the photo-catalyst, the air molecules generate cavities with strong oxidization, namely surface hydroxylation, and the energy is equivalent to a high temperature of 15,000K and can directly kill bacteria and decompose the organic substances into nontoxic and harmless substances such as CO2 and H2O. This technology has the following disadvantages: the optical-catalysis is restrained by the illumination intensity and the air flow, as the inactivation of the TiO2 itself is the fundamental reason for the efficiency decline of the photo-catalytic purification; Furthermore, the ultraviolet rays easily leak and can injure the skin and eyes of the human body.
The existing plasma air sterilizing and purifying device generally consists of a reactor, a high-voltage power supply, a fan component, a control unit, an air inlet, an air outlet, a power adaptor and a housing case; air filters are installed at the air inlet and the air outlet, and the plasma reactor is located in the air flow. The plasma reactor mainly comprises positive electrodes, negative electrodes and a housing case. The positive electrode has several structures, such as metal wires, saw teeth or needle tips. The mechanism of the plasma air sterilizing and purifying device is as follows: The plasma is a gas cloud which consists of a great amount of positive and negative charged particles and neutral particles; it has combined functions of the whole electric field and charges with quasi-neutrality. The plasma can severely break down and damage the cell membranes of bacteria and break the molecular bonds of the gas to generate radicals such as monatomic molecules, negative oxide ions, OH ions, free oxygen atoms and H2O2, which have strong activation and oxidation capabilities. It has a good effect in killing bacteria and viruses. It also can decompose such macromolecular toxic organics as formaldehyde, benzene, radon, ammonia, carbon monoxide, smoke and TVOC and convert them into nontoxic and scent-free inorganic substances such as carbon and water. The plasma reactor has an electrostatic field which can absorb particles with a minimum particle size of 0.1 um to further purify the air.